This invention relates generally to a decorative laminate having improved opacity, and more particularly, but not by way of limitation, to a decor sheet with high opacity at reduced basis weight and reduced ash.
High-pressure decorative laminates are laminated articles comprising plural layers of synthetic resin impregnated paper sheets consolidated or bonded together into a unitary structure under high heat and pressure. Conventionally, these laminates are made up of a plurality, e.g., seven or eight, of core or body sheets of a fibrous cellulose material, usually unbleached kraft paper, a decor sheet overlying the core sheets which cover the core sheets so that the brown paper of the core is not seen through the decor sheet, an optional but often used low basis weight overlay sheet, and an optional backing sheet. The decor sheet is usually made of high quality cellulose fiber impregnated with a thermosetting condensation resin such as a melamine formaldehyde resin.
These sheets are impregnated with resin and bonded together to form the decorative laminatae. Resins used may be any selected from phenolics, aminoplasts, polyesters, polyurethanes, epoxy resins and the like. Consolidation of the layers to a unitary laminated structure may involve pressures ranging from essentially zero (with contact only between the layers comprising the final laminate) to 2000 lbs. per sq. in. or more. Curing or setting of the resins may be accomplished at room temperature, or elevated temperatures (of the order of 150.degree.-180.degree. C.) to reduce the time required for curing.
For many applications it is necessary to maintain a level of opacity in the decor sheet to cover the core layers. This has been accomplished by adding opacifying pigments such as titanium dioxide to the paper furnish for the decor sheet to provide a controlled level of opacity. Titanium dioxide has been one of the most effective opacifiers for use in decorative laminates, however, titanium dioxide is expensive and it would be desirable if another filler or an agent of a different character could be used in conjunction with reduced amounts of titanium dioxide in forming decorative laminates without sacrificing the opacity of the decor sheet. Conventional fillers like clay, talc, silica, aluminum trihydrate (ATH), etc., have been employed in the decor sheets but are usually accompanied by a loss of opacity. One reason for this is that melamine formaldehyde has a refractive index very similar to fibers and fillers such as clay, talc, silica, and ATH. The overall refractive index becomes identical reducing potential fiber filler interfaces and thereby decreasing opacity.
There is therefore a need for a filler or extender which can be used in conjunction with titanium dioxide or other opacifying pigments in a decor sheet, without sacrificing a loss of opacity.